The normal processing of information by an integrated circuit (IC) may be upset by atmospheric disturbances. During the normal processing of information by an IC, outputs may be generated at pins of the IC from internally stored state and from inputs received at pins of the IC. An atmospheric upset may cause corruption of the internally stored state, for example, the value stored in a bit of the internal state may be inverted from the proper value for normal operation. The inverted bit of internal state may immediately or subsequently cause improper outputs to be generated at the pins of the IC. An atmospheric upset may be a soft failure that disrupts normal operation temporarily, and normal operation of the IC may be restored following, for example, a reset of the IC.
Example causes of atmospheric upsets include cosmic radiation and high-energy atomic particles from radioactive decay. An atomic particle of cosmic radiation from outer space may enter the Earth's atmosphere and collide with an atom above the IC. This collision and a cascade of subsequent secondary collisions may release a narrow stream of atomic particles including electrically charged atomic particles. The narrow stream of atomic particles may impact a memory or register cell for a bit of the internal state of the IC and deliver enough electric charge to the cell to invert the value stored in the cell from the proper value for normal operation.
The disruption of normal operation by atmospheric upsets affects the reliability of the IC. During the design of an IC, various design alternatives may affect the ultimate susceptibility of the subsequently fabricated IC to atmospheric upsets. Achieving the target reliability for the IC may require an appropriate selection of design alternatives. Further, users of the IC may request an accurate reliability specification. However, generating an accurate reliability specification may be delayed because of the time necessary to collect data for a statistically significant number of atmospheric upsets.
The present invention may address one or more of the above issues.